This invention relates to optical fibre assemblies for blown installation and more particularly to such assemblies as disclosed in EP-A-0345968 and EP-A-0521710 (to which reference is directed) in which the assembly comprises an optical fibre unit having at least one coated optical fibre. The coating includes at least one coating. The fibre unit has a coating comprising an external layer disposed over an inner, buffer layer, the external layer containing particulate matter which projects from the outer surface of that layer.
Like EP-A-0521710, this invention is particularly concerned with such assemblies in which the optical fibre unit comprises a plurality of coated optical fibres. Nevertheless, it is also applicable to such assemblies in which the optical fibre unit comprises just one optical fibre as in the illustrated embodiments of EP-A-0345968 where the coating of the optical fibre includes two coatings--a soft primary buffer coating and a hard secondary coating.
In EP-A-0345968 the particulate matter is mixed with the material of the external coating prior to application of that coating. However, this leads to the presence of the particulate matter at the interface between the external layer and the inner buffer layer which, it is concluded in EP-A-0521710, is the probable cause of poor "fibre breakout" performance on bending. This is particularly the case when the system of EP-A-0345968 is applied to such optical fibre assemblies in which the optical fibre unit comprises a plurality of coated optical fibres and thus need to have larger diameters than assemblies in which the fibre unit comprises a single optical fibre.
To overcome this problem of poor fibre breakout performance, EP-A-0521710 adds the particulate matter to the external layer after it has been applied. Therefore, the innermost part of the layer is substantially free of the particulate matter.